1. Field of the Invention
The present invention relates to an antistatic adhesive sheet. More particularly, the present invention pertains to an antistatic adhesive sheet which is excellent in antistatic properties and transparency, suppresses the bleed out of an antistatic agent and the generation of a gas, is capable of suppressing the adhesion of dirt, dust and the like, and the occurrence of a variety of troubles due to static electricity by sticking to an adherent so as to prevent the electric charging thereof, and in particular, is well suited for antistatic purpose of use in the products and articles that are required for transparency for a cover sheet.
2. Description of the Related Arts
A material having high insulation resistance such as plastics and the like has such a property that accumulates the static electricity which is generated by the friction or peeling between plastic and plastic or between plastic and an other object without leaking said electricity, that is, being electrically charged. The aforesaid property brings about not only unfavorable adhesion of dirt, dust and the like contained in the air, sticking of paper and paper or of film and film, uncomfortable feeling by an electric shock, but also various troubles and malfunctions such as erroneous actions and destroy of a memory due to static electricity, when used in electronic or electrical equipment and machinery, office automation equipment and machinery or the like.
In order to avoid such troubles or malfunctions, it is necessary to control the surface specific resistivity of an object to be charged, and thus an antistatic agent is usually employed.
As antistatic methods for a plastic product, there are generally available a method in which an antistatic agent is internally added (kneading) to the product, and a method in which an antistatic agent is applied to the surface thereof. Although the former method has favorable durability of antistatic effect, it suffers from the disadvantage that it is more prone to impair the characteristics inherent in plastics. On the other hand, although the latter method does not impair the characteristics inherent in plastics, it suffers from the drawback of inferiority in durability of antistatic effect.
An antistatic adhesive tape has heretofore been known, and is used in taping job to be carried out at the time of packaging and storing electronic part items that are sensitive to static electricity, specifically, sealing of a shield back, sealing of a carton, holding a worksheet, bundling electroconductive trays and the like. Moreover, a transparent antistatic adhesive tape is useful, for instance, as a sticking sheet for partitions and windows of a clean room, machine covers and various vessels used there, etc. in a factory and laboratory in the fields of electronic or electrical equipment and machinery, bionics, medicals, communication equipment and machinery, and the like. The aforesaid tape is also useful as a label for a hard disc used for a personal computer and as a protective sheet for an optomagnetic disc. In general, said optomagnetic disc is of the structure in which a transparent substrate is equipped thereon with a recording layer, on which is installed a protective layer. The writing and reading of information on said disc is carried out by laser light, which is irradiated via the substrate, and forms a focus on the recording layer. Dirt, dust or the like, when being adhered to or injures the substrate in such optomagnetic disc, becomes the cause for erroneous operation due to the deviation of a focus by the scattering-actions of the laser light or the like. In particular, since the beam bundle for reading out has the tendency to be miniaturized, further importance has been attached to the antistatic treatment and scratch resistance treatment on the surface of the substrate.
The above-mentioned antistatic adhesive tape and adhesive sheet are generally of the structure in which an adhesive agent layer is formed on one side of a plastic substrate film to which is internally added an antistatic agent, or of the structure in which an adhesive agent layer is formed on one side of a plastic substrate film, and an antistatic layer is formed on the opposite side thereof. The aforesaid adhesive agent layer is usually superimposed thereon with a release sheet for the purpose of protecting said adhesive agent layer.
As mentioned hereinbefore, however, the plastic substrate film to which an antistatic agent is internally added, has a fear of impairing the characteristics inherent in plastic substrate film. On the other hand, an antistatic layer which is formed on the opposite side of the adhesive agent layer brings about the problem that the adhesivity between said antistatic layer and, for instance, an easy-to-print layer or a scratch resistance coat layer, is extremely worsened in the case where such a layer is formed on said antistatic layer. In addition, when said antistatic layer is devoid of any cover layer thereon, there is caused a fear of unfavorable circumstances such that the antistatic agent bleeds out and a gas is generated therefrom. Such phenomenon is particularly remarkable in the case of a low molecular antistatic agent.
Under such circumstances, a general object of the present invention is to provide an antistatic adhesive sheet which is excellent in antistatic properties and transparency, suppresses the bleed out of an antistatic agent and the generation of a gas, is capable of suppressing the adhesion of dirt, dust and the like, and the occurrence of a variety of troubles due to static electricity by sticking said sheet to an adherent so as to prevent the electric charging thereof, and in particular is well suited for antistatic purpose of use in the products and articles that are required for transparency for a cover sheet.
Other objects of the present invention will be obvious from the text of this specification hereinafter disclosed.
As a result of intensive extensive research and investigation accumulated by the present inventors in order to develop an antistatic adhesive sheet having the foregoing excellent functions, it has been found that the objects of the invention are achieved by forming a plastic substrate film on one side with an antistatic layer comprising a quaternary ammonium salt, especially a high molecular type quaternary ammonium salt, and further forming thereupon, an adhesive agent layer. The present invention has been accomplished by the aforestated findings and information.
That is to say, the present invention provides an antistatic adhesive sheet comprising a plastic substrate film, an antistatic layer which is formed on either side thereof and which comprises a quaternary ammonium salt, preferably a high molecular type quaternary ammonium salt, and an adhesive agent layer formed on said antistatic layer.